Java把文件链接转成流，返回给前端下载

背景：已知Java拿到了一个PDF链接（http://xxx.xxx.pdf），直接把链接返给前端的话，前端是不能点击直接下载的，需要后端先把url转成文件流，再由前端下载，处理如下：
导入pom：

<dependency><groupId>org.apache.pdfbox</groupId><artifactId>pdfbox</artifactId><version>2.0.24</version></dependency>

接口部分：

@GetMapping("/downloadPdf")publicvoiddownloadPdf(@RequestParamString patentId,HttpServletResponse response)throwsIOException{String pdfLink ="http://xxx.xxx.pdf";URL url =newURL(pdfLink);try(InputStream inputStream = url.openStream();PDDocument document =PDDocument.load(inputStream)){// 设置响应头
            response.setContentType("application/pdf");
            response.setHeader("Content-Disposition","attachment;");// 写入响应流try(OutputStream outputStream = response.getOutputStream()){
                document.save(outputStream);}}}

前端部分：

downloadPDF(){let url = baseURL +"/xxx/xxx/downloadPdf?patentId="+this.patent_id;// 对应后端接口
      console.log(url);axios({
        method:'get',
        url: url,
        responseType:'blob',// 不加的话会白页
        headers:{'Authorization':'Bearer '+getToken()}}).then(response=>{const blob =newBlob([response.data]);const url =URL.createObjectURL(blob);const link = document.createElement('a');
          link.href = url;
          link.download =`xxx.pdf`;// 下载的文件名字
          link.click();});}

这样前端一点击，就能直接下载。

以上只适用于PDF，如下方式更万金油：

URL url =newURL(fileSrcUrl);HttpURLConnection connection =(HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
connection.connect();InputStream inputStream =newBufferedInputStream(connection.getInputStream());ByteArrayOutputStream outputStream =newByteArrayOutputStream();byte[] buffer =newbyte[1024];int bytesRead;while((bytesRead = inputStream.read(buffer))!=-1){
    outputStream.write(buffer,0, bytesRead);}byte[] fileBytes = outputStream.toByteArray();String fileName = url.getFile().substring(url.getFile().lastIndexOf('/')+1);HttpHeaders headers =newHttpHeaders();
headers.add("Content-Disposition","attachment; filename="+ fileName);returnnewResponseEntity<>(fileBytes, headers,HttpStatus.OK);

前端轮询下载结果：

downloadFile(){
      let url =this.baseUrl +"/baidu-translate/status?requestId="+this.requestId;axios({
        method:'get',
        url: url,
        responseType:'blob',
        headers:{'Authorization':'Bearer '+getToken()}}).then(res =>{
        console.log(res)if(res.status ===201){
          console.log('等待两秒再重试')setTimeout(this.downloadFile,3*1000);}else{// 文件下载const blob =newBlob([res.data],{
            type:'application'})// 获得文件名称
          let link = document.createElement('a')
          link.download =this.fileName
          link.style.display ='none'
          link.href = URL.createObjectURL(blob)
          document.body.appendChild(link)
          link.setAttribute('download',this.fileName)
          link.click()
          URL.revokeObjectURL(link.href);
          document.body.removeChild(link);
          link =null;this.loading =false}}).catch(err =>{
        console.log(err)this.$message.error('翻译失败，请稍后再试');this.loading =false})}